Backing disk for abrasive sheet



July 4, 1961 D. P. HACKETT BACKING DISK FOR ABRASIVE SHEET 2Sheets-Sheet 1 Filed July 10, 1958 INVENTOR. DONALD Pf/ACKETI 2 M QMATTORNEY D. P. HACKETT BACKING DISK FOR ABRASIVE SHEET July 4, 19 1 2Sheets-Sheet 2 Filed July 10, 1958 ,INVENTOR. DONALD PhAc/arz' ATTORNEYUnited States Patent 2,990,661 BACKING DISK FOR ABRASIVE SHEET Donald P.Hackett, 325 Pennsylvania Ave., Plymouth, Ind. FiledJuly 10, 1958,SenNo. 747,605 2 Claims. ((51. 51-197) This invention relates toimprovements in backing disks for abrasive sheets, and moreparticularlyto a power driven rotary disk having a face thereof spannedby an abrasive sheet adapted to be pressed against the face of a workpiece to smooth or abrade said surface.

The primary object" is to provide a backing disk of this character whichis simple in construction, inexpensive, easy to use, strong instructure, light in weight, readily mounted. and dismounted from a drivemember and accommodating rapid application of an abrasive sheet theretoand removal of an abrasive sheet therefrom.

A furtherobject is to. provide a backing disk' of this character havinga plurality of ribs, having sheet abutting portions lying insubstantially a common plane and having intervening offset portions,each provided with an aperture remote from the edge of the disk toaccommodate air flow through the space between said offset portion andan abrasive disk or sheet carried by said backing disk. I

A further object is to provide adevice of this character formed of heatconductive material and providing a support for an abrasive sheet atspaced points of that sheet and accommodating air flow between saidabrasive sheet and intervening portions of said backing disk, wherebyrapid heat transfer can occur from the working surface engaged by saidabrasive sheet and from said abrasive sheet. n A further object is toprovide a rotatable backing disk with a plurality of ribs adapted tosupport an abrasive sheet and intervening offset portions forming airpockets having air passages at the inner portions thereof and havingrecessed outer edges between said ribs to facilitate air flow into saidpockets.

A further object is to provide a rotatable backing disk for abrasivesheets, having a plurality of sheet contacting ribs extending from thecentral portion to the periphcry of said disk, and intervening offsetportions, together with a. recessed central portion receiving the headof a member for securing the abrasive sheet to the disk, and acentralreinforcement for said disk to rigidify the same, wherein said ribs areso shaped and proportioned as to facilitate batting and grinding of awork surface and to reduce choking of the abrasive surface of theabrasive sheet. by paint and soft metal forming a part of" that surfaceby virtue of freedom of portions of said sheet between. said ribs fromcontact with said backing disk. l A further object is to provide arotatable backing disk for abrasive sheets which is adapted to be drivenat high speed, which provides support for said backing sheet at limitedareas of said sheet including narrow areas extending from. the center tothe edge thereof and which exposes to air for cooling purposes theportions of the back of the sheet intervening between said last namednarrow disk portion.

Other objects will be apparent from the following specification.

In the drawing:

FIG. 1 is a perspective view of a backing disk mounted upon a power tooland supporting an abrasive sheet in operative position thereon;

FIG. 2 is a face view of the backing disk having an abrasive sheetapplied thereto which abrasive sheet is cut away at a part to exposesaid backing disk;

FIG. 3 is an edge view of the backing disk having an abrasive sheetsupported thereon;

2,990,661 Patented July 4, 1961 FIG. 4 is an edge view of a modifiedembodiment of the invention illustrating the mounting of a backing sheetthereon;

FIG. 5 is an enlarged sectional view taken on line 5-5 of FIG. 2;

FIG. 6 is a fragmentary face view of a modified form of the backingdisk;

FIG. 7 is a fragmentary detail sectional view taken on line 77 of FIG.6;

FIG. 8 is a face view of another modified embodiment of the backingdisk; and

FIG. 9 is a fragmentary detail sectional view taken on line 99 of FIG.8. 1

Referring to the drawing which illustrates the preferred embodiments ofthe invention, the numeral 10 designates a rotatable power driven shaftupon which my improved backing disk is adapted to be mounted. The shaft10 may be driven in any suitable manner, and in the form selected forillustration said shaft 10 constitutes the output shaft of a powerdriven hand tool having a motor housing 12 and grip portions 14 and 16and a shaft journaling sleeve or collar 18, from which the end of theshaft 10 projects in the usual manner.

My improved backing disk 20 is formed of rigid sheet metal or platestock or of any suitable rigid strong material preferably having theproperty of rapid heat transfer. I prefer to use sheet metal, such assteel or an aluminum alloy which is of substantially uniform thicknessthroughout. The disk 20 is of generally circular outline but ispreferably provided with a plurality of spaced recessed or scallopededge portions 22 preferably equally spaced and similar. Rib orsheet-contacting portions 24 are arranged symmetrically and extend fromthe outer edge of the disk 20 between adjacent scallops or recesses 22and the inner portion or central portion of the-disk. As here shown theportions 24 extend substantially radially and are of substantiallyuniform cross sectional configuration throughout their length, but itwill be understood that said portions 24 need not be straight nor radialnor of uniform cross-sectional shape along their length and need notextend continuously from the center to the edge of the disk. The crestportions of the ribs 24 are positioned outwardly with respect to theposition in which the disk is mounted on the shaft 10 and liesubstantially in a common plane to provide a planar backing. or supportat a plurality of points of an abrasive sheet 26. The abrasive sheet maybe the usual sandpaper, emery cloth or other material of sheet characterhaving abrasive particles adhered to one surface thereof. The centralportion of the disk 20 is preferably cupped as by theprovision of afrusto conical wall portion 28 and a central wall portion 30 rearwardlyoffset from the plane of the crest of the ribs 24. The disk has acentral opening. therein to receive the shank 32 of a securing member,suchas a securing screw which is screw-threaded in a central bore 34formed in the end of the shaft 10. The securing member preferably has athin flat head portion 36 whose axial dimension is less than the amount.of the offset 28 and which preferably is of large size compared to thediameter of the shank 32 so as to accommodate overlapping and marginalclamping of a substantial portion of the abrasive sheet 26 at the centerthereof, as best seen in FIG. 5.

The segmental portions 40 of the disk 20 between the ribs 24 arerearwardly offset from the peripheral edge of said disk to a pointadjacent to but spaced from the disk offset 28, thereby providing anannular portion 42 of the disk which is substantially coplanar with thecrests of the ribs 24. Each segmental offset 40 has an aperture 44formed therein at the inner portion thereof adjacent to the annularportion 42.

If desired, the disk 20 may be reinforced at the center thereof by areinforcing plate or sheet 50, as illustrated at FIG. 4, whichreinforcing plate may be welded or otherwise suitably secured to thedisk.

The abrasive sheet 26 is secured to the backing disk 20 concentricallythereof by means of the securing member 32, 36, as illustrated at FIG.5, with the abrasive surface thereof outermost or oppositely orientedwith respect to the backing sheet so as to engage the work surface inthe manner well understood in the art. The anchoring of the sheet at therecessed portion 28, -30 of the disk tends to deform the abrasive sheet26, but upon application of said sheet to a working surface the sheettends to assume substantially flat form at the marginal portion thereof,as illustrated in FIGS. 3, 4 and 5, with the back face of the abrasivesheet 26 bearing against the annular portion 42 of the disk and thecrests of the ribs 24.

In the use of the device, as the abrasive sheet is applied to theworking surface, the sheet accomplishes the desired butfing, grinding orsurfacing operation in the conventional manner, and accomplishes thiswork as rapidly as the work is accomplished by the use of prior knownbacking disks which provide greater surface area or contact between theabrasive disk and themselves. In other words, despite the fact that theportions of the sheet 26 which register with the segmental offsets 40lack direct backing from the disk, the abrasive sheet servessatisfactorily the grinding and buffing function intended for it, andaccomplishes that function as rapidly as it can now be accomplished bythe use of other types of backing disks.

As the backing disk and abrasive sheet mounted thereon are rotated bythe power driven shaft during the application thereof to the workingsurface, air is free to fiow in the segmental passages between the sheet26 and the segmental disk portions 40 and for the full depth of saidsegmental portions by reason of the provision of the central openings44. In other words, air flows between the peripheral edge of the diskand the openings 44. The recessed or scalloped configuration of the edgeportions 22 of the disk serve to enhance or facilitate air flow into thepassages between the sheet 26 and the offset disk portions 40 becausethe radially projecting portions at the ribs of the scalloped edgesdefine air scoops at the periphery of the disk. This air flow serves tocarry away the heat generated by the buffing or grinding or othersurfacing operation incident to the contact of the abrasive with thework pieces. The heat is carried away effectively because a largeportion of the abrasive sheet is directly exposed to the flow of airtherepast. Likewise the heat which passes through the abrasive sheetfrom the working surface to the disk at the ribs 24 and annular portion42 thereof is readily dissipated by this air flow passage. Still afurther efliciency of heat dissipation is accomplished by reason of theturbulence of the air at the back surface of the disk incident torotation of the disk.

I have found that by the use of a disk of this character the elfectivelife of an abrasive sheet of conventional character is greatlyincreased, that is, is increased many fold. In other words, whereasabrasive sheets commonly have a very short life when applied to bufiing,grinding and polishing operations when done by power driven tools, theirlife and full efiectiveness remain or continue as much as sixfold longerthan usual when used with a backing sheet of this character. I attributethis increase of effective life to the disk configuration and toundamped vibration which occurs during use incident to contact of theabrasive sheet with the work principally at the rib backed parts of thesheet incident to the application of grinding pressure during use and tothe rapid dissipation of heat generated by the abrading operation. Inother words, the bonding agent for the abrasive upon the abrasive sheetis protected against loss of efficiency due to high heat generation andtherefore retains and bonds or adheres the abrasive particles for muchlonger periods of time than occur in cases where the heat of the opera-4 tion is not dissipated suificiently rapidly to avoid deterioration ofthe bonding properties of the bonding agent.

Another interesting characteristic of abrasive sheets mounted upon myimproved backing disk is that they tend to be self-cleaning. It is acommon experience of the users of abrasive sheets operated by power tofind that the sheets clog rapidly and lose their abrasive propertieswhen working on work pieces having paint surfaces or having soft metalportions upon the working surfaces, such as portions of solder or brass.These materials, such as soft metal or paint seem to choke up theabrasive surface of the sheet and to seat in cavities between abrasiveparticles upon the sheet, thereby destroying the abrasive efiiciency ofthe abrasive sheet. This choking action is not experienced when abrasivesheets are applied to my improved backing disk, as in cases where theabrasive sheet is used in bufling and grinding automobile panels to berefinished. This advantage results from the vibration mentioned aboveand the fact that, when any tendency toward such choking action occurs,it can be corrected by applying the abrasive sheet against a steelsurface free of paint, solder and other clogging material and operatingthe backing disk to rotate the same for a short period of time until thebacking disk and the abrasive sheet have vibrated enough to rid theabrasive face of the abrasive sheet of accumulated clogging material.The abrasive sheet so applied against a sheet of steel tends to cleanitself rapidly and to restore its abrasive eflicieney when mounted uponmy improved disk. Thus it is possible to accomplish a bufling andgrinding operation more rapidly than can be done with abrasive sheetsmounted upon conventional backing disks, because the operator is notrequired to stop the work periodically for the purpose of replacingdisks which have choked due to collection of paint and soft metal in theabrasive surface thereof.

One additional advantage of the construction is its light weightresulting from its fabrication from thin stock. This is advantageousfrom the standpoint of reducing the efiort or energy required during usethereof and from the standpoint of reduction of the mass thereof to aminimum for the purpose of maintaining at a minimum the heat storagecapacity thereof. The reduction of heat storage capacity facilitates therapid heat dissipation which has been mentioned above.

The ribs may be formed of different cross-sectional configurations. Thusin the construction seen in FIG. 3, the ribs 24 have substantially flatcrest portions providing an area of contact between the same and thedisk 26. Such fiat faced ribs are not required, however, and instead theribs may be of curved cross-setcional shape, as illustrated at 24' inFIG. 4. I have found that the backing disk is substantially equallyefiicient in both configurations of the ribs.

Another embodiment of the invention is illustrated in FIGS. 6 and 7wherein the openings 44 between the ribs 24 of the disk are enlarged,and the area of the offset portions 40 of the disk between the ribs 24is reduced. This construction provides a large area of opening foraccess of air to the back of the disk and at the same time maintains therigidifying and supporting function of the offset portions 40 of thedisk.

It is not essential that the device maintain the shape of a disk, andinstead the device may assume the shape of a star wheel or a spider, asillustrated in FIG. 8, wherein the metal between the rib or spokeportions 24 is cut away completely. The parts 24 are bent transverselyto define marginal flanges projecting angularly from the plane of thedisk and of the abrasive sheet which bears thereagainst similarly to thearrangement shown in FIG. 4. In this instance the cross-sectionalconfiguration or curvature of the parts 24, together with the high speedof operation by the power driven tool, are relied upon to maintain thenecessary rigidity and support for the abrasive sheet- While thepreferred embodiments of the invention have 5 been illustrated anddescribed, it will be understood that changes in the construction may bemade within the scope of the appended claims without departing from thespirit of the invention.

I claim:

1. A backing member for an abrasive sheet, c0mprising a thin member ofsubstantially uniform thickness throughout formed of shape-retainingsheet metal having a central aperture and a plurality of integralelongated oifset ribs extending from the central portion to the edge ofsaid member, said ribs projecting substantially the same distance and inthe same direction from one face thereof and being arranged insubstantially equi-angular and equispaced relation to contact the backface of a substantially flat abrasive sheet at spaced narrow elongatedportions and thereby expose the intervening portions of the back face ofsaid sheet to air, said member having apertures therein between saidribs, the edges of said member between said ribs having concave curvededge portions.

2. A rotatable power-driven backing disk for an abrasive sheet,comprising a thin metal plate of substantially 6 I uniform thicknesshaving a plurality of elongated ofiset rib portions extending from theedge to the central portion of said member and adapted to engage andsupport spaced narrow elongated portions of an abrasive sheet, theportions of said member intervening between said ribs being offset fromthe plane of said sheet to provide air passages behind said sheet, andan aperture formed in each offset portion spaced from the periphery ofsaid member, said ribs being of substantially uniform crosssectionalshape throughout their length and said offset portions being of taperedshape from their outer to the inner ends and having concave curved edgeportions between said ribs.

References Cited in the file of this patent UNITED STATES PATENTS2,331,861 Smith Oct. 12, 1943 2,410,812 Michel Nov. 12, 1946 2,527,762Pratt Oct. 31, 1950 2,556,434 Mitchell June 12, 1951 2,819,568 KasickIan. 14, 1958

